Electronic postage meters have been developed with electronic accounting circuitry. Postage meter systems of this type are disclosed in U.S. Pat. No. 3,978,457 for Microcomputerized Electronic Postage Meter System and in U.S. Pat. No. 3,938,095 for Computer Responsive Postage Meter. The electronic accounting circuits include memory capability for storing postage accounting information. The memory function in the electronic accounting circuits have replaced the function served in postage meters by mechanical accounting registers.
Postage meters with mechanical accounting registers are not subject to many of the problems encountered by electronic postage meters. Conditions cannot normally occur in postage meters with mechanical registers that prevent accounting for a printing cycle or which result in the loss of data stored in the registers. Thus, dependent reliable control of the postage printing mechanism operation is desirable in electronic postage meters. It is also desirable in systems of this type that the printing mechanism be controlled in a manner which inhibits printing postage if the system is not operating properly.
Postage meter printing systems suitable for use with electronic postage meters, such as those disclosed in U.S. Pat. No. 3,965,851 for Setting Mechanism for a Postage Printing Device and U.S. Pat. No. 4,050,374 for Meter Setting Mechanism, include a printing drum with a set of adjacent print wheels each of which carriers print characters. Each print wheel is set for example, to position different postage amounts for printing, by an independently rotatable gear mechanism adapted to be engaged by a master gear. The master gear is rotatably mounted within a laterally movable carriage. The carriage can be moved to cause successive engagement with each independently rotatable gear mechanism. The printing drum is energized to rotate to print postage by a drive gear within the meter. Meter printing systems of this type are detachably mounted on a drive base. When so mounted, the postage meter drive gear meshes with a drive gear in the base. One suitable drive base is disclosed in U.S. Pat. No. 2,934,009 for Sheet Feeding and Treating.
Postage meter printing systems may incorporate a shutter bar movably mounted within the meter. The shutter bar is movable into and out of a blocking position which inhibits energization of the postage meter drive gear. When the meter is mounted on the base, the shutter bar is mechanically connected to a shutter bar lever on the base which drives the shutter bar to move into and out of the blocking position. A clutch is provided in the base and is operated by the shutter bar lever. The clutch is arranged to prevent the base drive gear from rotating unless the shutter bar lever is in a position which corresponds to the shutter bar being moved out of the blocking position. This insures that if the base is tripped to drive the postage meter drive gear, the base drive gear will rotate only if the shutter bar has been moved by the shutter bar lever out of its blocking position.
The postage setting meter printing systems of the above type may also incorporate interposers which prevent the shutter bar from being moved out of its blocking position by the drive base shutter bar lever. The interposers may be operated to lock the shutter bar in the blocking position and thereby inhibit energization of the meter drive gear when the postage meter is not properly conditioned to print postage. For example, in U.S. Pat. No. 4,050,374 for Meter Setting Mechanism, the shutter bar is blocked by a camming extension on the master gear carriage or yoke when the carriage is shifted to any position other than an enable position. These arrangements are satisfactory and properly perform their intended purpose.